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Problems with the Voltage Regulation Module VRM
Hey everyone,
We had an issue with one of the VRMs on our test robot last week where the radio would intermittently drop the driver station, but maintain communication with our debug PC. We're using LabVIEW on our robots this year. The DS would drop while idling, moving, enabling, etc. which seemed odd. In past years teams would have issues with communication dropping because of a loose cable, a bad connection, bad soldering, etc. but I can't ever recall seeing a bad voltage regulation module at a competition. I swapped radios and still experienced the same issue, so I decided to remove the VRM and replace it with last year's module (remember, this is a test robot). I finally had a chance to test the module in the lab and found quite a few issues with it. I used a high power decade resistor box as my load, a calibrated Keithley power supply set at 12.3V/1.5A as my source, a calibrated Fluke multimeter to verify the resistance of the decade resistor box, and a calibrated Tek oscilloscope to capture the waveforms. TEST 1: 5 V / 2A Output Load: 3 ohms (measured) - Calculated current: 1.6A
![]() Screenshot of test 1's waveform. Note that the oscilloscope is set to AC coupling. Test 2: 5 V / 2 A Output Load: 4 ohms (measured) - Calculated current: 1.25A
![]() Screenshot of test 2's waveform. Note that the oscilloscope is set to AC coupling. Test 3: 5 V / 2 A Output Load: 10 ohms (measured) - Calculated current: 500mA
![]() Screenshot of test 3's waveform. Note that the oscilloscope is set to AC coupling. Conclusion It looks like there is something seriously wrong with this module. I'm planning on taking similar data on another VRM in order to compare the results. I really hope we don't have to walk around with oscilloscopes at champs! |
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